National Board Inservice Inspector (NB-IS)
Certification Exam Questions With Correct
Answers (Verified Answers) Plus Rationales
2026 Q&A | Instant Download Pdf
1. Which of the following is the primary purpose of inservice
inspection of boilers and pressure vessels?
A. Design optimization
B. Preventive maintenance
C. Safety and regulatory compliance
D. Cost reduction
Rationale: Inservice inspections ensure that boilers and pressure
vessels are operating safely and in compliance with applicable codes,
preventing accidents and failures.
2. The National Board Inservice Code is found in which document?
A. ASME B31.1
B. NB-IC (National Board Inspection Code)
C. API 510
D. OSHA Boiler Regulations
,Rationale: The National Board Inspection Code (NB-IC) provides
requirements for inservice inspection, repair, and alteration of boilers
and pressure vessels.
3. During an internal inspection, a boiler shell exhibits a dent that is
4% of its diameter. How should this be evaluated?
A. Ignore it if no leak is present
B. Repair immediately
C. Assess according to NB-IC acceptance criteria
D. Replace the entire shell
Rationale: The NB-IC provides acceptance criteria for dents, buckles,
and other deformations, including evaluation based on depth,
location, and effect on structural integrity.
4. What is the minimum thickness for which ultrasonic thickness
testing is generally reliable on carbon steel?
A. 0.05 in
B. 0.10 in
C. 0.12 in
D. 0.20 in
Rationale: Ultrasonic thickness testing is accurate for carbon steel
plates typically greater than 0.12 inches, allowing inspectors to
determine wall loss due to corrosion.
, 5. The term “hydrostatic test” refers to which of the following?
A. Testing using steam under pressure
B. Filling the vessel with water and applying pressure
C. Applying vacuum to the vessel
D. Using air to check for leaks
Rationale: Hydrostatic testing involves filling a vessel with water and
pressurizing it to detect leaks and verify structural integrity. Water is
used because it is incompressible, reducing explosion risk.
6. During inspection, pitting corrosion is observed on the internal
surface of a vessel. The inspector should:
A. Paint over the pits
B. Measure depth and compare to NB-IC limits
C. Drill holes to relieve stress
D. Ignore it
Rationale: Pitting corrosion can significantly reduce wall thickness.
The NB-IC specifies allowable limits and evaluation methods to
determine if repair or continued service is permitted.
7. Which of the following is the most common cause of boiler tube
failure?
A. Overpressure
B. Manufacturing defects
, C. Corrosion and overheating
D. Improper installation
Rationale: Corrosion and overheating are primary causes of boiler
tube failures, leading to thinning, scaling, or rupture, making them
critical inspection focus areas.
8. For a pressure vessel in operation, the inspection interval for a full
internal examination is:
A. Annually
B. Every 2 years
C. Every 5 years or as specified by NB-IC
D. Only when repairs are needed
Rationale: The NB-IC specifies inspection intervals based on vessel
type, service, and risk; a full internal inspection is generally required
every 5 years, though more frequent checks may be necessary in
aggressive environments.
9. What does “corrosion allowance” mean in the context of pressure
vessel design and inspection?
A. Extra margin for fabrication errors
B. Extra margin for thermal expansion
C. Extra thickness to compensate for expected corrosion
D. Extra safety factor for pressure
Certification Exam Questions With Correct
Answers (Verified Answers) Plus Rationales
2026 Q&A | Instant Download Pdf
1. Which of the following is the primary purpose of inservice
inspection of boilers and pressure vessels?
A. Design optimization
B. Preventive maintenance
C. Safety and regulatory compliance
D. Cost reduction
Rationale: Inservice inspections ensure that boilers and pressure
vessels are operating safely and in compliance with applicable codes,
preventing accidents and failures.
2. The National Board Inservice Code is found in which document?
A. ASME B31.1
B. NB-IC (National Board Inspection Code)
C. API 510
D. OSHA Boiler Regulations
,Rationale: The National Board Inspection Code (NB-IC) provides
requirements for inservice inspection, repair, and alteration of boilers
and pressure vessels.
3. During an internal inspection, a boiler shell exhibits a dent that is
4% of its diameter. How should this be evaluated?
A. Ignore it if no leak is present
B. Repair immediately
C. Assess according to NB-IC acceptance criteria
D. Replace the entire shell
Rationale: The NB-IC provides acceptance criteria for dents, buckles,
and other deformations, including evaluation based on depth,
location, and effect on structural integrity.
4. What is the minimum thickness for which ultrasonic thickness
testing is generally reliable on carbon steel?
A. 0.05 in
B. 0.10 in
C. 0.12 in
D. 0.20 in
Rationale: Ultrasonic thickness testing is accurate for carbon steel
plates typically greater than 0.12 inches, allowing inspectors to
determine wall loss due to corrosion.
, 5. The term “hydrostatic test” refers to which of the following?
A. Testing using steam under pressure
B. Filling the vessel with water and applying pressure
C. Applying vacuum to the vessel
D. Using air to check for leaks
Rationale: Hydrostatic testing involves filling a vessel with water and
pressurizing it to detect leaks and verify structural integrity. Water is
used because it is incompressible, reducing explosion risk.
6. During inspection, pitting corrosion is observed on the internal
surface of a vessel. The inspector should:
A. Paint over the pits
B. Measure depth and compare to NB-IC limits
C. Drill holes to relieve stress
D. Ignore it
Rationale: Pitting corrosion can significantly reduce wall thickness.
The NB-IC specifies allowable limits and evaluation methods to
determine if repair or continued service is permitted.
7. Which of the following is the most common cause of boiler tube
failure?
A. Overpressure
B. Manufacturing defects
, C. Corrosion and overheating
D. Improper installation
Rationale: Corrosion and overheating are primary causes of boiler
tube failures, leading to thinning, scaling, or rupture, making them
critical inspection focus areas.
8. For a pressure vessel in operation, the inspection interval for a full
internal examination is:
A. Annually
B. Every 2 years
C. Every 5 years or as specified by NB-IC
D. Only when repairs are needed
Rationale: The NB-IC specifies inspection intervals based on vessel
type, service, and risk; a full internal inspection is generally required
every 5 years, though more frequent checks may be necessary in
aggressive environments.
9. What does “corrosion allowance” mean in the context of pressure
vessel design and inspection?
A. Extra margin for fabrication errors
B. Extra margin for thermal expansion
C. Extra thickness to compensate for expected corrosion
D. Extra safety factor for pressure
